which of the following statements best describes the exothermic reaction below?

ID: 704161 • Letter: W

Question

which of the following statements best describes the exothermic reaction below? and why not the other options? how can I know?

2HCL (aq) + Na2C)3 (s) > 2 NaCL (aq) + CO2 (g) + H2O (l)

a. the reaction is always spontaneous

b. the reaction is spontaneous at "low" temperatures but not "high" temperatures

c. the reaction is spontaneous at "high" temperatures but not "low" temperatures

d. the reaction is never spontaneous

e. not enough information is given

part B;

at what temperature (in celsisu) does a reaction start/stop being spontaneous if the reaction has a delta Hrxn= -210.5 kj/mol and delta S=-128j/molk?

a. always spontaneous

b. 1371

c. 1645

d. 1918

e. never spontaneous

2HCl (aq) + Na2CO3 (s) -----------> 2 NaCl (aq) + CO2 (g) + H2O (l)

The above reaction is a neutralisation reaction and heat energy is liberated.

So, dH = -ve

And during the reaction entropy is increased due to evolution gaseous product CO2.

So, dS = +ve

Now, dG = dH - TdS

Since dH = -ve, dS = +ve

=> therefore, dG = -ve

As dG = -ve, the reaction is spontaneous.

Hence, answer is option (a).

Part (B) :

dHrxn = -210 kJ/mol , and dS = -128 J/mol.K = -0.128 kJ/mol.K

we know that, dG = dH - TdS

For a spontaneous reaction dG = -ve

T < dH / dS

T < -210.5 / -0.128

T < 1645 K

T < 1371 0C

at 1371 0C temperature the given reaction stop being spontaneous. Below 1371 0C , the reaction is spontaneous.

Therefore answer is option (b).

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